Medicinal inhalation devices, including pressurized inhalers, such as metered dose pressurized inhalers (MDIs), and dry powder inhalers (DPIs), are widely used for delivering medicaments.
Medicinal inhalation devices typically comprise a plurality of hardware components, (which in the case of a MDI can include gasket seals; metered dose valves (including their individual components, such as ferrules, valve bodies, valve stems, tanks, springs retaining cups and seals); containers; and actuators) as well as a number of internal surfaces which may be in contact with the medicinal formulation during storage or come in contact with the medicinal formulation during delivery. Often a desirable material for a particular component is found to be unsuitable in regard to its surface properties, e.g. surface energy, and/or its interaction with the medicinal formulation. For example, the relatively high surface energy of materials typically used in MDIs, e.g. acetal polymer for valve stems, or deep drawn stainless steels or aluminum for containers, can cause medicament particles in suspension formulations to adhere irreversibly to the surfaces of corresponding component(s), which has a consequent impact on the uniformity of medicinal delivery. Similar effects are also observed for DPIs. Other examples of potentially undesirable interactions between a component and the medicinal formulation may include enhanced medicament degradation; adsorption of medicament or permeation of a formulation constituent or extraction of chemicals from plastic materials. For DPIs often permeation and adsorption of ambient water pose issues. Also the use of materials having relatively high surface energy for certain components (e.g. metered dose valves and/or individual components thereof), may have undesirable effects for the operation of movable components of a medicinal inhalation device.
Various coatings have been proposed for particular components or surfaces of metered dose inhalers, see e.g. EP 642 992, WO 96/32099, WO 96/32150-1, WO 96/32345, WO 99/42154, WO 02/47829, WO03/024623; WO 02/30498, WO 01/64273; WO 91/64274-5; WO 01/64524; and WO 03/006181.